The present invention is a process for preparing powder of high temperature oxide superconductors of Bi-Pb-Sr-Ca-Cu-O type.
In conventional processes, high temperature metal oxide superconductors are prepared by conventional solid state reaction. That is, the oxides or carbonates of the metal moieties ultimately desired in the final metal oxide superconductors are mixed in an appropriate ratio, ground, calcined, and sintered to obtain oxide superconducting materials. However, the final product obtained in this conventional process is a coarse powder(grain size larger than 1 um) and poor in uniformity, which seriously affects its subsequent applications.
The drawbacks of the above process can be improved by employing a method of metal co-precipitation in which more uniform in size and finer particulates of precursor powder can be obtained. In this process, oxalate precipitation reagent is added to an aqueous solution comprising soluble salts of the desired metals. Sodium hydroxide (or potassium hydroxide) is added to the solution to adjust its pH value in order to form oxalate co-precipitants of the Bi-Pb-Sr-Ca-Cu-O mixture. The coprecipitant is then filtered, dried, and sintered. The addition of sodium and/or potassium hydroxide to the solution will simultaneously change its pH. Although the co-precipitant can be obtained rapidly, the co-precipitate is not uniform. Besides, due to the residue of the sodium and/or potassium ions, the superconductivity of the products thus obtained is affected. Sometimes, ammonium oxalate is used as the precipitant reagent, however the pH of the solution cannot be adjusted. Thus, in this conventional process, the proportion of individual components of co-precipitate are rather difficult to be controlled, and the process is inappropriate for use in mass production.